1. Field of the Invention
The present invention relates to an apparatus for displaying isotope radiation distribution images, which is employed with a scintillation camera used in nuclear medicine, and more particularly to improvements in the display systems for a scintillation camera system that employs a plurality of detector heads.
2. Description of the Prior Art
When radiation emitted from a radioactive isotope introduced into a foreground subject is conducted to a scintillator through a collimator, the scintillator gives forth fluorescent rays. Since the position of the scintillation point corresponds to the position of a radioactive isotope present in the foreground subject, the plane distribution of the radioactive isotope is observed in the form of an image of light given forth by the scintillator.
In general, such an image is usually reproduced on the screen of a cathode ray tube, as a momentary spot of light at a point spatially corresponding to the position from which radiation emanates from a subject. Each unit of detected radiation is individually displayed, one at a time, as a dot on the cathode ray tube screen. A composite of many such dots recorded photographically forms an image of the radioisotope distribution in the subject.
A well-known scintillation camera is described in U.S. Pat. No. 3,011,057, issued Nov. 28, 1961, for Radiation Image Device, to Hal O. Anger. Systems and methods for recording the distribution of a radioactive substance on X-ray film are described in U.S. Pat. No. 4,115,693 and U.S. Pat. No. 4,075,485.
A detector head includes a scintillator for giving forth fluorescent rays upon absorption of radiation emitted from a radioactive isotope taken into the foreground subject and a plurality of photomultipliers for detecting fluorescent rays from the scintillator through a light guide and converting the rays to electrical signals.
A given scintillation results in a number of simultaneous output signals from the photomultipliers. These electrical signals are amplified and processed by electrical circuitry which is, in turn, connected to a cathode ray tube (CRT). These signal are processed and applied to the horizontal and vertical deflection circuits of the CRT. Signals corresponding to the intensity of a given scintillation, termed Z axis signals, are also processed by the circuitry for permitting production of an electron beam in the CRT. The processing circuitry also includes a pulse height analyzer, which determines whether a detected scintillation has resulted from radiation within a desired energy level range. If a given scintillation is within a desired intensity level range, the pulse height analyzer circuitry permits the CRT to produce an electron beam which is deflected in accordance with the output signals from X and Y axis summing and ratio circuits which result from that scintillation. The X and Y axis summing and ratio circuits produce X and Y axis signals having a pulse height respectively corresponding to the position of the scintillation point along the X and Y axes. An illuminated point or spot on the CRT screen is thus produced at a location on the screen which corresponds to the X and Y location of the scintillation in the scintillator crystal.
There is also a control signal supplied from the scintillation camera to the CRT, termed a START/STOP signal, which allows the X-ray film to be exposed with the cathode ray tube for a predetermined period of time or a predetermined count operating at a lower level value. Corresponding with each START/STOP signal, by adding a predetermined offset voltage to the X and Y axis signals, the CRT beam is deflected to create an image at a desired area on the CRT screen and a plurality of individual images are exposed on a single frame of X-ray film.
However, in the emission CT system which is described in U.S. Pat. No. 3,970,853, issued July 20, 1976, for a Transverse Section Radionuclide Scanning System, or in the radioisotope imaging system combining a stationary scintillation camera with a mobile scintillation camera, the individual images taken at the same time by a plurality of detector heads would not be displayed on a single screen of the CRT and be exposed on a single frame of the X-ray film.